This application claims priority to Japanese patent application serial number 2001-337948, the contents of which are incorporated herein by reference.
1. Technical Field
The present invention relates to variable displacement compressors. More particularly, the present invention relates to techniques for suitably controlling the pressure within a drive chamber of a variable displacement compressor.
2. Description of the Related Art
U.S. Pat. No. 6,212,893 teaches an air conditioning system that includes a variable displacement compressor, a cooling circuit, a heating circuit, a displacement control valve and a controller. The cooling circuit includes a condenser, a first expansion valve and an evaporator, which are disposed within a circuit extending from an outlet of the compressor to an inlet of the compressor. Therefore, highly pressurized refrigerant is discharged from the compressor and is then drawn into the compressor via the elements in the circuit line. The refrigerant is repeatedly circulated through the air conditioning system in order to perform a cooling operation.
The heating circuit includes a bypass path that connects the outlet to the evaporator. The heating circuit also includes a second expansion valve disposed within the bypass path and the above-described evaporator. Therefore, high temperature and highly pressurized refrigerant discharged from the compressor may be drawn into the compressor via the second expansion valve and the evaporator without being circulated to the condenser. This cycle also may be repeatedly performed in order to perform a heating operation. In general, this type of heating circuit is known as xe2x80x9chot gas heater.xe2x80x9d By opening and closing a switching valve, switching between the cooling circuit and the heating circuit can be performed.
The displacement control valve is disposed within a communication path between the outlet for the pressurized refrigerant and a drive chamber defined within a housing of the compressor. The controller serves to open the displacement control valve in order to increase the pressure within the drive chamber when the pressure of the discharged refrigerant exceeds a reference value.
However, if the displacement control valve is actuated so as to open when the pressure of the discharged refrigerant exceeds the reference value, the pressure within the drive chamber may unintentionally increase excessively, if the environmental temperature is relatively high or the amount of refrigerant remaining within the heating circuit is relatively large. Therefore, the pressure within the drive chamber may exceed a durable limit pressure of a sealing mechanism, such as a seal lip, that communicates with the drive chamber. The drive chamber will more likely exceed the durable limit pressure when the heating circuit is operated rather than when the cooling circuit is operated, because the discharge pressure of the refrigerant during the operation of the heating circuit is normally higher than the discharge pressure of the refrigerant during the operation of the cooling circuit.
Therefore, pressure control techniques have been developed so as to maintain the pressure within the drive chamber within a predetermined range, thereby ensuring the durability of the lip seal even during the operation of the heating circuit. As a result, the pressure within the drive chamber can be adjusted to an appropriate pressure (or appropriate pressure range) in view of the durability of the lip seal by appropriately varying the maximum discharge pressure (i.e., a reference value for the discharge pressure) based upon pressure fluctuation factors, such as environmental temperature.
Therefore, it is one object of the present invention to teach improved techniques for suitably controlling the pressure within the drive chamber of a variable displacement compressor, which includes a displacement control valve for controlling refrigerant output displacement.
According to one aspect of the present teachings, variable displacement compressors are taught that may include a displacement control valve that is in communication with a drive chamber. The refrigerant output displacement of the compressor generally varies in response to changes in pressure within the drive chamber. A controller may actuate the displacement control valve in order to maintain the pressure within the drive chamber within a predetermined range. The predetermined range may be determined based upon factors that cause fluctuations in the pressure within the drive chamber during the operation of the compressor. For example, such factors may include, e.g., the environmental temperature of the compressor, the temperature of an air conditioning circuit associated with the compressor, and the driving speed, i.e., the rotational speed of the compressor.
In another aspect of the present teachings, the compressors may include parts or devices, e.g. a sealing device for a drive shaft, which communicate with the drive chamber. Such parts or devices may have a durable limit pressure. That is, if the pressure within the drive chamber exceeds a certain pressure, such parts may be damaged and operation of the compressor may deteriorate. Therefore, by appropriately actuating the displacement control valve such that the pressure within the drive chamber does not exceed the durable limit pressure of the target part or device, the present compressors can reliably operate without applying excessive pressure to the target part or device.
In another aspect, the compressors may include a discharge chamber that communicates with the drive chamber via the displacement control valve. In this case, a refrigerant may be compressed within the compressor and then may be delivered or supplied to the drive chamber via the displacement control valve. The controller may select a reference value for the pressure of the discharged refrigerant based upon the nature of the pressure fluctuation factors and changes in the values of the pressure fluctuation factors. Therefore, the displacement control valve may be controlled or actuated based upon such a reference value.
According to another aspect of the present teachings, air conditioning systems are taught that include one of the variable displacement compressors that include the above features.
According to another aspect of the present teachings, methods for controlling variable displacement compressors are taught that may include, e.g., (1) determining a predetermined pressure range for a drive chamber defined within the variable displacement compressor based upon one or more factors that may possibly cause (excessive) pressure fluctuations within the drive chamber and (2) actuating a displacement control valve, which communicates with the drive chamber, in order to maintain the pressure within the drive chamber within the predetermined pressure range.